The present invention relates to a voltage control oscillator (VCO) used in the mobile communication systems such as cellular phones and car phones, and visual machines and satellite installations, in more particular, to a high frequency dual band output oscillator used by changing an operation and non-operation of the frequency band due to externally applied control voltage.
Nowadays, various communication machines such as cellular phones usable by plural communication systems called a dual mode have been popularized, so that different frequency bands are used and a number of the kind of frequency increases, resulting in a broadening of the frequency bands of voltage control oscillators of local oscillating machines determining the frequency to be used.
In particular, the dual modes cellular phones are necessary to oscillate a plurality of frequencies and it is necessary to cover the necessary frequency band by using a plurality of voltage control oscillators of single mode, or a voltage control oscillator of dual mode.
For example, in the USA AMPS system and DMA system, and in Europe GSM system and DCS system are employed as frequency band systems.
By the way, Japan Patent Laid-open gazette H9(1997)-294018 and U.S. Pat. No. 5,852,384 describe a high frequency dual band oscillator circuit generating signals of two different frequency bands.
The conventional high frequency dual band oscillator circuit described in these official gazettes has a first oscillator circuit functioning an oscillation operation in the first frequency band, a second oscillator circuit functioning an oscillation operation in the second frequency band, and a buffer amplifier circuit into which an output of the first oscillator circuit enters through the first stage-to-stage coupling capacitor and into which an output of the second oscillator circuit enters through the second stage-to-stage coupling capacitor.
When an oscillation output is taken out of the first frequency band, it is necessary to apply a base voltage of the oscillation transistor constructing the first oscillation circuit through the first base bias control terminal to the conventional high frequency dual band oscillator circuit. If another base voltage of an oscillation transistor constructing the second oscillator circuit is not applied to the conventional high frequency dual band oscillator circuit from the second base bias control terminal, only the first oscillation circuit becomes active generating an oscillation output, this oscillation output is amplified by the buffer amplifier circuit through the first stage-to-stage coupling capacitor and the output amplified is taken out of the high frequency output terminal.
While, in order to take out an oscillation output from the second frequency band, it is necessary to apply a base voltage of the second base bias control terminal to the conventional high frequency dual band oscillation circuit. Because that a base voltage is not applied from the first base bias control terminal to the oscillation circuit, only the second oscillation circuit becomes operative condition and an oscillation output of the second oscillation circuit is amplified in the buffer amplifier circuit through the second stage-to-stage coupling capacitor and the amplified oscillation output is taken out through a high frequency output terminal.
According to the high frequency dual band oscillation circuit of an old type, two buffer amplifier circuits were necessary for two frequency bands respectively. In the conventional high frequency dual band oscillation circuit described in the two official gazettes, the oscillation output is amplified with one buffer amplifier circuit.
The conventional high frequency dual band oscillation circuit above is able to decrease the number of the buffer amplifier circuit from two to one, however two of the first and second base bias control terminal are necessary and additionally two logic circuits for controlling respective these base bias control terminals and two control circuits for controlling respective two tuning voltage supply terminals are necessary to have a function for controlling a timing of an operation and non-operation of the first and second oscillation circuits and also every oscillation circuit is necessary to have the emitter resistor of the oscillation transistor. As a result, the number of parts increases prohibiting whole size of the mechanism from miniaturizing and a power for the external logic and control circuits is necessary disadvantageously increasing the power to be consumed.
Consequently, the present invention provides the high frequency dual band oscillation circuit of no fault, having parts of small number which is attained by making the circuits in common and switches of simple structure, resulting in a small size of the whole machine, a low consuming power, and a low manufacturing cost
The high frequency dual band output oscillator of the present invention has a first output oscillation circuit operating in an oscillation manner at a first frequency band, a second output oscillation circuit operating in an oscillation manner at a second frequency band, one broad band buffer amplifier circuit into which an oscillation output of the first output oscillation circuit enters through a stage-to-stage coupling element and an oscillation output of the second output oscillation circuit enters through frequency selective filters and the stage-to-stage coupling element, and a switch terminal controlling an operation or a non-operation of one of the first and second output oscillation circuits. The broad band buffer amplifier circuit is constructed with a buffer amplifier circuit and an impedance matching circuit placed at the back stage of the buffer amplifier circuit, and the high frequency dual band output oscillator has a structure so constructed as to selectively output an oscillation signal from the first and second output oscillation circuit when a control voltage is externally applied or not applied to the switch terminal. As a result, two base bias control terminals which are necessary to each output oscillation circuit and two logic circuits for controlling these base bias control terminals, which circuits are necessary, have been necessary to the conventional high frequency dual band oscillation circuit.
According to the high frequency dual band oscillation circuit of the present invention, it is possible to reduce the number of such logic circuits and base bias control terminals to one, respectively decreasing the number of parts.
According to the high frequency dual band output oscillator of the present invention, the emitter side of an oscillation transistor of one of the first and second output oscillation circuits is connected with an emitter resistor or another oscillation transistor through an inductor of the frequency selective filter, and another emitter resister of another oscillation transistor is commonly used for the emitter resistor of the former oscillation transistor. Consequently, it is possible to reduce the number of two emitter resistors of the oscillation transistor, which are necessary to each of two oscillation circuits to one, and reduce the number of whole parts of the conventional high frequency dual band output oscillator. As a result, according to the present invention, it is possible to miniaturize the machine size, decrease the manufacturing cost, and saving the power operating the installation.